How we test dehumidifiers

Clearing the fog

Last updated: 17 August 2018

If you're trying to beat indoor dampness – especially in cold weather – you might be scratching your head over whether a dehumidifier is the answer and which one to choose. Do they really live up to their claims, and how will they cope in winter when it's harder to extract moisture from the air?

We test dehumidifiers to help you choose the best one for your needs. Here's how we go about it.

Our expert testers

CHOICE maintains a highly professional NATA-accredited laboratory and the vast majority of our product testing is done in-house. However some tests, including dehumidifiers, demand particular expertise and equipment that we don't have, so in these cases we engage an accredited external lab to do the testing according to our requirements.

How we choose what we review

With so many to choose from, what makes us choose one dehumidifier to test over another? Like with most of our product testing, our aim is to test the most popular models on the market and what you're most likely to see in the retailers.

We survey manufacturers to find out about their range of dehumidifiers, we check market sales information and we also check for any member requests to test specific models. From this information we put together a final list that goes to our buyers. They then head out to the retailers and buy each product, just as a normal consumer would. We do this so we can be sure the machines are the same as any consumer would find them and not 'tweaked' in any way.

How we test

Water removal and energy efficiency

The dehumidifiers are set up in a temperature- and humidity-controlled test chamber. For each model, the lab measures the amount of water removed during three test runs at different temperature/humidity combinations that reflect humid winter climates (at 8°C / 90% relative humidity; 12°C / 75% relative humidity; and 16°C / 65% relative humidity.). We found the best-performing models remove more than twice the volume of water compared with the worst at the coldest temperatures.

Cold, humid conditions present a worst-case scenario for most dehumidifiers, as they usually use refrigeration technology. It's easier for a refrigeration dehumidifier to extract moisture from warm air than from cold (which is why manufacturers usually quote removal rates at conditions that make their machines look the best – typically 30°C and 80% relative humidity), because it's easier for them cool hot air (in order to condense the water from it) than to further cool air that is already cold.

To see how a desiccant model compares with a refrigeration model in hot humid conditions, we conducted a one-off test in 30°C and 80% relative humidity, using a desiccant model and a refrigeration model that had each performed reasonably well in our tests.

Both performed OK and in line with their rated water extraction rate, but the refrigeration model extracted more than four times as much water in hot conditions as it did in cold conditions. See our buying guide for further explanation of what this might mean when choosing a dehumidifier for your own home.

When measuring the water removal, the lab also measures the energy consumption of the dehumidifier. From this we can calculate how many millilitres of water the model extracts from the air per watt of electricity used, and therefore how efficient the model is in comparison to others we're testing.

Ease of use

The lab testers assess each model for ease of accessing and emptying the water tank, quality of instructions and labels, using the controls, mobility of the unit and ease of cleaning it.

Noise

We measure the noise of the unit while it's running (these results are comparative only; what you actually hear depends on the environment). Most measure upwards of 50dB, enough to be potentially annoying if you're trying to watch TV or sleep.

Running costs

These are the approximate per hour cost of running the unit, and the electricity cost for the unit to extract 10 litres of water. The latter figure often shows that a model that uses less power, but is slow to extract water, can cost the same to run as a model with higher consumption but faster extraction.

Test criteria explained

The overall score is made up of:

Water removal (50%)

Energy efficiency (30%)

Ease of use (20%).

Our test lab

Testing dehumidifiers requires a very specific laboratory, as described above in How we test. While CHOICE does have high quality thermal laboratories, we don't have a lab suited to this particular testing – it would be very expensive to construct and maintain. So instead, when we review dehumidifiers we send them to a qualified external lab.